[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Andrew Svetlov]

Change by Andrew Svetlov :


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Andrew Svetlov]

Andrew Svetlov  added the comment:

Thanks, guys!

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[miss-islington]

miss-islington  added the comment:


New changeset 164dddf5f8c9c6b93f32c9f79b4301fc804576e9 by Miss Islington (bot) 
in branch '3.10':
bpo-45416: Fix use of asyncio.Condition() with explicit Lock objects (GH-28850)
https://github.com/python/cpython/commit/164dddf5f8c9c6b93f32c9f79b4301fc804576e9


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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[miss-islington]

Change by miss-islington :


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nosy: +miss-islington
nosy_count: 7.0 -> 8.0
pull_requests: +27163
pull_request: https://github.com/python/cpython/pull/28856

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:


New changeset 1a7892414e654aa5c99efa31db767baba7f4a424 by Joongi Kim in branch 
'main':
bpo-45416: Fix use of asyncio.Condition() with explicit Lock objects (GH-28850)
https://github.com/python/cpython/commit/1a7892414e654aa5c99efa31db767baba7f4a424


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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Joongi Kim]

Change by Joongi Kim :


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keywords: +patch
nosy: +Joongi Kim
nosy_count: 6.0 -> 7.0
pull_requests: +27160
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/28850

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Dong-hee Na]

Change by Dong-hee Na :


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versions: +Python 3.11

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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nosy: +serhiy.storchaka

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Łukasz Langa]

Łukasz Langa  added the comment:

Issue confirmed. The problem is that `Condition.__init__` compares its own loop 
with Lock's internal `_loop` attribute. That attribute is set to None unless 
the lock waited to be acquired.

uriyyo, Andrew, Yury, since it's pretty likely that Lock objects will now have 
`_loop` set to None, I think the check for "loop agreement" in Condition is 
kind of useless. So I propose to simply remove it. It's the only such check in 
all of asyncio.

If you insist on keeping the loop check, it should special-case `_loop is None`.

Simon, thanks for your detailed report! As a backwards-compatible workaround 
till we get a fix in, your user code can do the following:

>>> l = asyncio.Lock()
>>> getattr(l, '_get_loop', lambda: None)()
<_UnixSelectorEventLoop running=True closed=False debug=False>

You can use such lock without issues now:

>>> asyncio.Condition(l)


Alternatively, if the above disgusts you and you only want to trigger public 
APIs, you can do this dance:

>>> l = asyncio.Lock()
>>> await l.acquire()  # first acquire will just work
True
>>> try:
...   # second acquire will block so we time it out
...   await asyncio.wait_for(l.acquire(), 0.1)
... except asyncio.TimeoutError:
...   pass
...
>>> l.release()

Now the lock is fully initialized and we can use it:

>>> c = asyncio.Condition(l)

Both workarounds should be compatible with Python 3.7+ asyncio.

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nosy: +lukasz.langa, uriyyo

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Simon Willison]

Simon Willison  added the comment:

It looks like the relevant test is here: 
https://github.com/python/cpython/blob/a1092f62492a3fcd6195bea94eccf8d5a300acb1/Lib/test/test_asyncio/test_locks.py#L722-L727

def test_explicit_lock(self):
lock = asyncio.Lock()
cond = asyncio.Condition(lock)

self.assertIs(cond._lock, lock)
self.assertIs(cond._loop, lock._loop)

But... that test doesn't appear to run inside an event loop, so it's not 
covering the behaviour described in this issue.

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Simon Willison]

Simon Willison  added the comment:

I ran across this issue while trying to use the https://pypi.org/project/janus/ 
locking library with Python 3.10 - see my issue on their tracker here: 
https://github.com/aio-libs/janus/issues/358

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[issue45416] "loop argument must agree with lock" instantiating asyncio.Condition

[Simon Willison]

New submission from Simon Willison :

In Python 3.10 it is not possible to instantiate an asyncio.Condition that 
wraps an asyncio.Lock without raising a "loop argument must agree with lock" 
exception.

This code raises that exception:

asyncio.Condition(asyncio.Lock())

This worked in previous Python versions.

Note that the error only occurs if an event loop is running. Here's a simple 
script that replicates the problem:

import asyncio

# This runs without an exception:
print(asyncio.Condition(asyncio.Lock()))

# This does not work:
async def example():
print(asyncio.Condition(asyncio.Lock()))

# This raises "ValueError: loop argument must agree with lock":
asyncio.run(example())

--
components: asyncio
messages: 403500
nosy: asvetlov, simonw, yselivanov
priority: normal
severity: normal
status: open
title: "loop argument must agree with lock" instantiating asyncio.Condition
versions: Python 3.10

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